If you are adding the data to the data source using external logic then the grid should show the records as expected. You just need to ensure that the data is added to the database before data-binding the Grid.
With that said, would you send us a runnable sample where the behavior you are seeing is replicated? This will enable us to examine the issue and look for its cause.
Telerik by Progress
Telerik UI for ASP.NET AJAX is ready for Visual Studio 2017 RC! Learn more.